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Dinnu

Member Since: 24 Dec 2019
Location: Lija
Posts: 3208

2012 Defender 90 Puma 2.2 CSW Santorini Black

Dot5 fluid in a Defender

Gents, for my 90 restoration I have been pondering if I should use Dot5 for the brake and clutch hydraulic fluid. The only reason is because Dot5 does not eat paint.

There is a very good explanation by Oilman here: https://www.defender2.net/forum/topic4739.html?highlight=dot5

The main downsides are water that can pool and cause localized corrosion (can steam up as well) and lower lubrication.

Has anyone used Dot5 in his Defender, Series or any other classic car? If yes, were the above downsides serious that warrant not to use Dot5.

Once my restoration is completed, it will live in a warm garage, will avoid wet weather, will not go wading, and will not see high speeds. So the water/steam issue might not be that big for me.

Thoughts? 1988 90 Hard Top, 19J Diesel Turbo, Shire Blue - Restoration ongoing
2012 90 CSW, 2.2TDCI, Santorini Black

22nd May 2021 6:19am

90 Dreamer

Member Since: 13 Jul 2019
Location: Oop North
Posts: 2054

2016 Defender 90 Puma 2.2 HT Corris Grey

personally I wouldn't use it in anything...........it has long service life for things like extended military use where you may not want to service the vehicle due to "metalized rain" or other issues but its NOT a well performing fluid IMO

unless your planning on washing your truck in it just use a good quality dot4 / dot 5.1 fluid

22nd May 2021 8:40am

Bluest

Member Since: 23 Apr 2016
Location: Lancashire
Posts: 3997

2007 Defender 110 Puma 2.4 XS CSW Java Black

My Dad has used it in his gently driven MG for years with no apparent issues. I don’t actually know why he uses it, but he seems happy with it. 2007 110 TDCi Station Wagon XS

22nd May 2021 9:35am

Bluest

Member Since: 23 Apr 2016
Location: Lancashire
Posts: 3997

A bit off topic, but given brakes are hydraulic system, why don’t they use hydraulic oil? I guess it’s to do with viscosity through the tiny pipes, but not sure. 2007 110 TDCi Station Wagon XS

22nd May 2021 9:37am

Dinnu

Member Since: 24 Dec 2019
Location: Lija
Posts: 3208

90 Dreamer wrote:
personally I wouldn't use it in anything...........it has long service life for things like extended military use where you may not want to service the vehicle due to "metalized rain" or other issues but its NOT a well performing fluid IMO

unless your planning on washing your truck in it just use a good quality dot4 / dot 5.1 fluid

I read online that performance wise it is the lesser than the other dots. But how much less performance. 1%, 10% 50%? And when talking about performance is it braking power, or brake fade at high temperature?

My experience with LandRover hydraulic systems is not if it leaks but just when it will leak.
I am not a heavy brake user, I use a lot of engine braking. IIRC, the brake pads on the 90 lasted around 80kmiles. So probably temperature is not an issue for my use. 1988 90 Hard Top, 19J Diesel Turbo, Shire Blue - Restoration ongoing
2012 90 CSW, 2.2TDCI, Santorini Black

22nd May 2021 11:30am

Dinnu

Member Since: 24 Dec 2019
Location: Lija
Posts: 3208

Bluest wrote:
My Dad has used it in his gently driven MG for years with no apparent issues. I don’t actually know why he uses it, but he seems happy with it.

Yes, probably gentle is the key word here. It will have a 19J, so gentle will be. 1988 90 Hard Top, 19J Diesel Turbo, Shire Blue - Restoration ongoing
2012 90 CSW, 2.2TDCI, Santorini Black

22nd May 2021 11:31am

discomog

Member Since: 09 May 2015
Location: Notts/Lincs Border
Posts: 2496

2015 Defender 90 Puma 2.2 XS CSW Santorini Black

Yes viscosity due to small bore pipes and orifices is one reason. Another is that hydraulic oil absorbs oxygen bubbles and therefore is undesirable in a braking system the same as air in a braking system. Also hydraulic oil is flammable and therefore any fluid leak onto a hot brake disc could cause a fire. Defender 90XS SW
Mini Countryman Cooper S
Morgan Plus 8

22nd May 2021 11:37am

Pacha

Member Since: 23 Feb 2020
Location: North Yorkshire
Posts: 772

2008 Defender 90 Puma 2.4 HT Stornoway Grey

Bluest wrote:
A bit off topic, but given brakes are hydraulic system, why don’t they use hydraulic oil? I guess it’s to do with viscosity through the tiny pipes, but not sure.

Flammable, much lower temperature operating range. Rgds.

Chris

22nd May 2021 11:59am

90 Dreamer

Member Since: 13 Jul 2019
Location: Oop North
Posts: 2054

can confirm that Brake Fluid is also very flammable as are most fluids on a vehicle............ATF is another

22nd May 2021 12:46pm

RFT

Member Since: 13 Nov 2010
Location: Cheshire
Posts: 674

2010 Defender 130 Puma 2.4 HCPU Zermatt Silver

Bluest wrote:
A bit off topic, but given brakes are hydraulic system, why don’t they use hydraulic oil? I guess it’s to do with viscosity through the tiny pipes, but not sure.

Brake fluid is a type of hydraulic fluid, Hydraulic fluid is any fluid that transmits force by means of hydraulic pressure, water is a hydraulic fluid. 130 Puma HCPU with an Artica 240LR Demountable Camper

22nd May 2021 4:33pm

RFT

Member Since: 13 Nov 2010
Location: Cheshire
Posts: 674

Pacha wrote:
Bluest wrote:
A bit off topic, but given brakes are hydraulic system, why don’t they use hydraulic oil? I guess it’s to do with viscosity through the tiny pipes, but not sure.

Flammable, much lower temperature operating range.

There are many industrial Hydraulic oils with much higher operating temperature ranges as used in steel making, glass furnaces, cement plants.

Many of these oils have very low flammability, it takes an atomised spray from a very high pressure system to hit a hot surface or open flames for them to ignite, in my 5 years as a Steel Works Engineer I saw very few hydraulic leaks ignite fortunately but those i did see I'll never forget, the radiant heat given off by the flames is unbelievably hot. 130 Puma HCPU with an Artica 240LR Demountable Camper

22nd May 2021 4:48pm

Dinnu

Member Since: 24 Dec 2019
Location: Lija
Posts: 3208

Bluest wrote:
A bit off topic, but given brakes are hydraulic system, why don’t they use hydraulic oil? I guess it’s to do with viscosity through the tiny pipes, but not sure.

Forgot all about it, but many moons ago I used to have a Citroen BX. That the one with hydraulic suspension. The braking and suspension system used the same LHM fluid. Cannot recall if it was corrosive and paint damaging though. Quick google search seems to be a mineral oil. 1988 90 Hard Top, 19J Diesel Turbo, Shire Blue - Restoration ongoing
2012 90 CSW, 2.2TDCI, Santorini Black

22nd May 2021 8:53pm

Bluest

Member Since: 23 Apr 2016
Location: Lancashire
Posts: 3997

I think Rolls Royce used the same fluid as Citroen’s too, as they used a licensed version of the Citroen brake/suspension system 2007 110 TDCi Station Wagon XS

22nd May 2021 8:59pm

Pacha

Member Since: 23 Feb 2020
Location: North Yorkshire
Posts: 772

90 Dreamer wrote:
personally I wouldn't use it in anything...........it has long service life for things like extended military use where you may not want to service the vehicle due to "metalized rain" or other issues but its NOT a well performing fluid IMO

unless your planning on washing your truck in it just use a good quality dot4 / dot 5.1 fluid

I agree - whilst it might not be great for paintwork, why would this be a massive concern?

I cannot recall anytime in the last 40 years that I spilt brake fluid on the bodywork of any vehicle. Rgds.

Chris

22nd May 2021 9:25pm

Dinnu

Member Since: 24 Dec 2019
Location: Lija
Posts: 3208

^^^ True, brake pipes are very reliable. But I am more concerned about bulkhead/footwells. If the clutch master cylinder starts leaking, all the oil will go in the footwell. If not noticed early enough, due to carpets etc, that area would soon end up with soggy paintwork. The brake master cylinder is further out of the bulkhead and will only damage the paint on the servo.

Perhaps Dot5 for clutch (less critical component) and Dot4 for brakes!

I read online that military vehicle use Dot5, but the reason being that these vehicles are idle for very long periods, and they need to go in action without prior notice. So perhaps there is also other benefits for vehicles that are not used on a regular basis. Less chance that the brakes seize up?? 1988 90 Hard Top, 19J Diesel Turbo, Shire Blue - Restoration ongoing
2012 90 CSW, 2.2TDCI, Santorini Black

23rd May 2021 6:12am

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